 The mantle lengths of the common bobtail differ depending on gender, as males range 15 to 29mm whereas females range 18 to 34mm.The average length of a male common bobtail is 15 to 30mm, with females having an average of 18 to 36mm.The weight of a male common bobtail, between 0.1g - 0.7g.on average is more than a male common bobtail average, 0.2g - 1.4g in mass.